A DIFFERENT LOOK AT HURRICANE ANDREW-LIGHTNING AROUND THE EYEWALL
Randy Lascody
National Weather Service Office
Melbourne, FL
The track of hurricane Andrew in August 1992, was followed closely by millions of people through satellite and
radar observations. In fact , it was the first hurricane tracked
by a WSR-88D operated by the National Weather Service.
But is it possible that Andrew's track could have been followed through lightning detection equipment? This is precisely what the National Weather Service Office in Melbourne was able to do as Hurricane Andrew neared the
southeast Florida coast. A circular pattern in the lightning
was evident as Andrew moved across the warm Gulf Stream
waters clearly defining the eye of the hurricane!
Lightning data available at Melbourne are supplied by
Atmospheric Research Systems, Inc. (ARS!) through a dialin port. The data are obtained through the Lightning Position
and Tracking System (LPATS). This system uses a time-ofarrival technique to position cloud-to-surface strokes.
ARSI's software package, Video Information System (VIS),
allows display and manipulation of the lightning data.
Figure I shows the circular nature of the lightning pattern
as the hurricane moved across the Gulf Stream just east
of Miami. About 15 cloud-to-water strokes were detected
around the eye in a ten-minute period ending at 0743 UTC 24
August 1992. If we assume the lightning pattern is concentric
around the eye, the approximate eye position determined
from the lightning data is 25.so N, 79.9° W. The composite
reflectivity (in gray scale) from the Melbourne WSR-88D at
about the same time is shown in Fig. 2. Again , the eye
position is approximately 25.so N, 79.9° W. (This is easily
determined with the WSR-88D by positioning a cursor in the
center of the eye and reading the cursor location from the
information display as shown in Fig. 2 [CUR. LlLJ.)
Figure 3 is a composite of all cloud-to-surface lightning
strokes for the period 0149 UTC to 0849 UTC. Lightning
strokes associated with spiral bands were most numerous in
Andrew's south quadrant, and in time lapse they can be seen
rotating cyclonically inward toward the eyewall. Note that
far more lightning strokes were measured in spiral bands
away from the hurricane center as compared to the eyewall
region. Another feature that persisted as Andrew was nearing
Miami was that most of the cloud-to-surface lightning strokes
occurred over the water. There was one band well to the
north between Grand Bahama Island and West Palm Beach
that produced lightning over interior sections of Palm Beach
County.
Enhanced infrared satellite imagery indicated the convection around the center of Andrew increased considerably
just before landfall. According to NWS Southern Region
Forecaster Notes No.3 (1992) , if a tropical cyclone passes
over warmer water while other environmental conditions
remain the same, the warmer water may playa role in cyclone
intensification. Therefore, it seems possible that the increase
in convection around Andrew's center at landfall may have
been aided by warm Gulf Stream water. This is supported
by the extensive lightning associated with Andrew's spiral
bands and especially by the fact that lightning increased
around the eyewall as it moved over the Gulf Stream. On
the other hand, surface friction asymmetries may also have
played a role in thunderstorm (and lightning) generation as
the storm felt the effects of landfall.
This brief analysis of Andrew ' s lightning activity illustrates
a phenomena that much of the meteorological community
has not yet seen. In conversations with National Hurricane
Center and WSFO personnel , I learned that extensive lightning in hurricanes has not often been documented. Given
that Andrew is the most costly hurricane on record, I am
sure that more in-depth studies of this and other aspects of
the hurricane will be forthcoming .
Reference
NWS SOllthem Region Forecaster Notes No.3 , July 1992: Do
The Strongest Tropical Cyclones Occur Over The Warmest
Waters? Scientific Services Division, NWS Southern Region
Headquarters, Fort Worth , Texas.
Author
Randy Lascody entered the National Weather Service in
1986 at the Weather Service Forecast Office in Miami, Florida. He is currently at the National Weather Service Office
in Melbourne , Florida and has been there since 1990. Randy
received his Bachelor of Science degree in meteorology from
Northern Illinois University in December 1981. His special
interests include all aspects of operational forecasting, from
the synoptic scale to the unique Florida mesoscale environment.
39
National Weather Digest
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Fig . 1. 10 minute composite of cloud-to-water lightning strokes
ending at 0743 UTC 24 AUG 1992.
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Fig . 3. Composite of cloud-to-surface lightning strokes for period
0149 to 0849 UTC, 24 AUG 1992.
1(t 15 ,' $'Z 137'·20
CMP REF
38
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08 / 24 / 92 07 ' 58
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UNIT 1 READ DONE
HARDCOPY
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ACCEPTED
Fig . 2. Composite reflectivity from Melbourne WSR 880. 0750 UTC, 24 AUG 1992.
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